In recent years, the development of clean energy has become desirable due to global environmental concerns, such as the problems of energy resource depletion and increased CO2 levels in the atmosphere, etc. In particular, photovoltaic power generation (photovoltaic power generation systems), which uses solar cells, has been developed and put to practical use as a new energy source.
For photovoltaic power generation systems, cost reduction would be desirable in terms of achieving wider adoption and a photovoltaic power generation system that improves the amount of generated electrical power and decreases the per-unit cost of the generated electrical power by comprising a tracking drive section tracking sunlight and orienting solar cell modules to the solar azimuth and elevation has been proposed as one such approach.
Moreover, concentrator-type photovoltaic power generation systems are being developed, which decrease the cost of the entire photovoltaic power generation system by reducing the use of photovoltaic cells, i.e. the most expensive component in a photovoltaic power generation system (solar cell module), by generating electricity based on tracking the Sun and collecting the incident sunlight.
In order for them to play an auxiliary role of power stations supplying electric power not only to undeveloped areas and mountainous areas, but also to urban areas, and the like, it has been proposed to use these photovoltaic power generation systems as photovoltaic power generation systems connected to power converters (power conditioners) in order to allow them to be linked to the electric power system.
As for control methods used to control the tracking drive of photovoltaic power generation systems, a method has been disclosed in Patent document 1, in which the Sun is tracked by detecting the direction of the Sun using a solar position sensor. Moreover, a method has been disclosed in Patent document 2, in which the azimuth and elevation of the Sun are calculated based on the latitude/longitude and time/date at the site where a photovoltaic power generation system is installed, and the light receiving surfaces of the solar cell modules are oriented in that direction.
Moreover, similar methods are known in case of photovoltaic power generation systems utilizing concentrator-type solar cell modules, and a method, in which the direction of the Sun is detected from the output of a photo sensor and the light receiving surfaces of the solar cell modules are oriented to the solar azimuth and elevation, has been disclosed in Patent document 3. The only difference of concentrator-type modules is that they are constructed to collect sunlight with lenses and irradiate photovoltaic cells, which reduces the angular tolerance of the tracking shift angle and requires high accuracy in solar tracking. Their basic solar tracking operation, however, is similar to non-concentrator type photovoltaic power generation systems.    Patent Document 1: JP2000-196126A.    Patent Document 2: JP2002-202817A.    Patent Document 3: JP2004-153202A.